To achieve compatibility between a multi-channel system and a stereo technique, U.S. Pat. No. 5,638,451 discloses a transmission and storage method for audio signals. In this prior art method, signals from additional audio channels of the multi-channel audio system are added to the left and right basic signals of the multi-channel audio system, such that two modified stereo signals are created for reproduction via a stereo system.
US 2004/0141619 discloses a method of generating a left modified and a right modified audio signal for a stereo system from multi-channel audio signals with a left and a right channel and at least one further audio channel. In this prior art method, the signal of the channel of higher energy is modified in a filter with a transformation function in a first parallel branch and is modified in a second filter with a reverberation function in a second parallel branch, the modified signals being joined together in a summation unit.
WO2005/036925 discloses an apparatus for processing a multi-channel audio signal in a stereo compatible manner. This prior art apparatus comprises means for providing a first Lc and second Rc downmix channels derived from the original channels, Lc and Rc being defined as follows:Lc=t·(L+aLs+bC)Rc=t·(R+aRs+bC)
wherein t, a and b are weighted factors smaller than 1, L is an original left channel, C is an original center channel, R is an original right channel, Ls is an original left surround channel and Rs is an original right surround channel.